A magnetoresistive effect element is used for a magnetic head (for example, an MR head; a magnetoresistive head). The MR head is mounted on a magnetic recording and reproducing apparatus, and reads information from a magnetic recording medium such as a hard disk drive. To enhance the performance (recording density) of the hard disk, a technology utilizing the spin accumulation effect is desired as a high resolution reproducing head. In the technology utilizing the spin accumulation effect, there is room for improvement of the deficiency in the output voltage and spin injection efficiency.